Protective relaying generally involves the performance of one or more of the following functions in connection with a protected power or energy system: (a) monitoring the system to ascertain whether it is in a normal or abnormal state; (b) metering, which involves measuring certain electrical quantities; (c) protection, which typically involves tripping a circuit breaker in response to the detection of a short-circuit condition; and (d) alarming, which provides a warning of some impending problem. In connection with these and other ancillary functions, such as fault detection, detection of power flow direction, over-current detection, etc., the protective relaying system must compare phasor quantities (voltages and currents). Generally, the faster such a comparison can be made, the better.
Prior to the present invention, protective relays compared phasor quantities using frequency domain techniques such as the Fourier transform. A primary goal of the present invention is to provide methods and apparatus for comparing phasor quantities in real time.